Hydraulic system for working machine and control valve

ABSTRACT

A hydraulic system includes a first hydraulic device to be operated by an operation fluid, a second hydraulic device, the second hydraulic device being configured to be operated by the operation fluid, a first control valve to control the first hydraulic device, a second control valve disposed on a downstream side of the first control valve and configured to control the second hydraulic device, a communication tube connecting the first hydraulic device to the first control valve, the communication tube being configured to supply a return fluid that returns from the first hydraulic device to the first control valve, a supply fluid tube connecting the first control valve to the second control valve and being configured to supply the return fluid to the second control valve, and a connection fluid tube disposed on the first control valve, the connection fluid tube connecting the communication tube to the supply fluid tube.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2017-182585, filed Sep. 22, 2017, and to Japanese Patent Application No. 2017-097651, filed May 16, 2017. The contents of these applications are incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a hydraulic system for a working machine and to a control valve.

Discussion of the Background

Japanese Unexamined Patent Application Publication No. 2010-270527 discloses a hydraulic system for a working machine. The working machine disclosed in Japanese Unexamined Patent Application Publication No. 2010-270527 includes a boom, a bucket, a boom cylinder configured to operate the boom, a bucket cylinder configured to operate the bucket, an auxiliary actuator configured to operate an auxiliary attachment, a first control valve configured to control stretching and shortening of the boom cylinder, a second control valve configured to control stretching and shortening of the bucket cylinder, and a third control valve configured to operate the auxiliary actuator.

SUMMARY OF THE INVENTION

A hydraulic system of a working machine includes a hydraulic pump configured to output an operation fluid, a first hydraulic device configured to be operated by the operation fluid, a second hydraulic device other than the first hydraulic device, the second hydraulic device being configured to be operated by the operation fluid, a first control valve configured to control the first hydraulic device, a second control valve disposed on a downstream side of the first control valve and configured to control the second hydraulic device, a communication tube connecting the first hydraulic device to the first control valve, the communication tube being configured to supply a return fluid that returns from the first hydraulic device to the first control valve, a supply fluid tube connecting the first control valve to the second control valve, the supply fluid tube being configured to supply the return fluid to the second control valve, a connection fluid tube disposed on the first control valve, the connection fluid tube connecting the communication tube to the supply fluid tube, a discharge fluid tube connected to the first control valve, a setting portion disposed on the discharge fluid tube and configured to increase a pressure in the discharge fluid tube, a branching fluid tube branched from the connection fluid tube, the branching fluid tube being connected to the discharge fluid tube, and a throttle disposed on the branching fluid tube.

A hydraulic system of a working machine includes a hydraulic pump configured to output an operation fluid, a first hydraulic device configured to be operated by the operation fluid, a second hydraulic device other than the first hydraulic device, the second hydraulic device being configured to be operated by the operation fluid, a first control valve configured to control the first hydraulic device, a second control valve disposed on a downstream side of the first control valve and configured to control the second hydraulic device, a first communication tube connecting the first hydraulic device to the first control valve, the first communication tube being configured to supply a return fluid that returns from the first hydraulic device to the first control valve, a second communication tube other than the first communication tube, the second communication tube connecting the first hydraulic device to the first control valve and being configured to supply the return fluid that returns from the first hydraulic device to the first control valve, a supply fluid tube connecting the first control valve to the second control valve, the supply fluid tube being configured to supply the return fluid to the second control valve, a first connection fluid tube disposed on the first control valve, the first connection fluid tube connecting the first communication tube to the supply fluid tube, a second connection fluid tube other than the first connection fluid tube, the second connection fluid tube being disposed on the first control valve and connecting the second communication tube to the supply fluid tube, a discharge fluid tube connected to the first control valve, a first branching fluid tube branched from the first connection fluid tube, the first branching fluid tube being connected to the discharge fluid tube, a second branching fluid tube branched from the second connection fluid tube, the second branching fluid tube being connected to the discharge fluid tube, a first throttle disposed on the first branching fluid tube, and a second throttle disposed on the second branching fluid tube, the second throttle being smaller than the first throttle.

A control valve includes a first port to which a first fluid tube is connected, the first fluid tube being connected to a first hydraulic device, a second port to which a second fluid tube is connected, the second fluid tube being connected to the first hydraulic device, a third port to which a third fluid tube is connected, the third fluid tube being connected to a hydraulic pump configured to output an operation fluid, a fourth port to which a first discharge fluid tube is connected, the first discharge fluid tube being configured to discharge the operation fluid, a fifth port configured to discharge the operation fluid to an outside, the operation fluid having passed through the first port or the second port, a main body including a first inner fluid path, a second inner fluid path, a third inner fluid path, a fourth inner fluid path, and a fifth inner fluid path connected to the first port, the second port, the third port, the fourth port, and the fifth port, and a spool configured to move inside the main body to change communicating destinations of the first inner fluid path, the second inner fluid path, the third inner fluid path, the fourth inner fluid path, and the fifth inner fluid path and to move between a communicating position and a neutral position, the communicating position allowing the second inner fluid path and the fifth inner fluid path to be communicated with each other or the first inner fluid path and the fifth inner fluid path to be communicated with each other, the spool including a first communicating portion configured to allow the second inner fluid path and the fourth inner fluid path to be communicated with each other or the first inner fluid path and the fourth inner fluid path to be communicated with each other when positioned between the communicating position and the neutral position.

A hydraulic system of a working machine includes a hydraulic pump configured to output an operation fluid, a first hydraulic actuator, a second hydraulic actuator, a first control valve including an input port into which the operation fluid to be supplied to the first hydraulic actuator is introduced, the first control valve being configured to control the first hydraulic actuator by the operation fluid to be supplied, a second control valve disposed on a downstream side of the first control valve and configured to control the second hydraulic actuator, a first fluid tube configured to connect the first control valve to the second control valve and to supply a return fluid to the second control valve, the return fluid returning from the first hydraulic actuator to the first control valve, a second fluid tube other than the first fluid tube, the second fluid tube being configured to connect the first control valve to the second control valve and to be communicated with the first fluid tube, and a third fluid tube configured to be communicated with the second fluid tube and to return the return fluid of the first fluid tube to the input port.

DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

FIG. 1 is a view illustrating a hydraulic system (a hydraulic circuit) according to a first embodiment of the present invention;

FIG. 2 is a view illustrating a modified example of the hydraulic system (the hydraulic circuit) according to the first embodiment;

FIG. 3 is a view illustrating a hydraulic system (a hydraulic circuit) according to a second embodiment of the present invention;

FIG. 4A is a view illustrating an inside of a control valve being in a neutral position according to the second embodiment;

FIG. 4B is a view illustrating the inside of the control valve being in a position between the neutral position and a first position according to the second embodiment;

FIG. 4C is a view illustrating the inside of the control valve being in the first position according to the second embodiment;

FIG. 5 is a view illustrating a hydraulic system (a hydraulic circuit) according to a third embodiment of the present invention; and

FIG. 6 is a view illustrating a whole of a skid steer loader exemplified as a working machine according to the embodiments.

DESCRIPTION OF THE EMBODIMENTS

The embodiments will now be described with reference to the accompanying drawings, wherein like reference numerals designate corresponding or identical elements throughout the various drawings. The drawings are to be viewed in an orientation in which the reference numerals are viewed correctly.

First Embodiment

FIG. 6 shows a side view of a working machine 1 according to embodiments of the present invention. FIG. 6 shows a skid steer loader as an example of the working machine. However, the working machine according to the embodiments of the present invention is not limited to the skid steer loader, but may be another kind of the loader working machine such as a compact track loader or the like. Further, the working machine may be another working machine other than the loader work machine.

The working machine 1 includes a machine body (a vehicle body) 2, a cabin 3, a working device 4, a traveling device 5A, and a traveling device 5B.

The cabin 3 is mounted on the machine body 2. An operator seat 8 is disposed at a rear portion of an inside of the cabin 3. In explanations of the embodiments of the present invention, a front side (a left side in FIG. 6) of the operator seated on the operator seat 8 of the working machine 1 is referred to as the front (a front side), a rear side (a right side in FIG. 6) of the operator seated on the operator seat 8 of the working machine 1 is referred to as the rear (a rear side), a left side (a front surface side in FIG. 6) of the operator seated on the operator seat 8 of the working machine 1 is referred to as the left (a left side), and a right side (a back surface side in FIG. 6) of the operator seated on the operator seat 8 of the working machine 1 is referred to as the right (a right side). In addition, a horizontal direction corresponding to a direction perpendicular to the front-to-rear direction will be referred to as a machine width direction. A direction extending from the center portion of the machine body 2 to the right portion or the left portion will be referred to as machine outward. In other words, the machine outward is a machine width direction that corresponds to a direction separating away from the machine body 2. In the explanation, a direction opposite to the machine outward is referred to as a machine inward. In other words, the machine inward is a machine width direction that corresponds to a direction approaching the machine body 2.

The cabin 3 is mounted on the machine body 2. The working device 4 is a device configured to perform a work, and is mounted on the machine body 2. The traveling device 5A is a device configured to allow the machine body 2 to travel, and is disposed on the left side of the machine body 2. The traveling device 5B is a device configured to allow the machine body 2 to travel, and is disposed on the right side of the machine body 2. A prime mover (a motor) 7 is disposed at a rear portion of an inside of the machine body 2. The prime mover 7 is a diesel engine (an engine). Meanwhile, it should be noted that the prime mover 7 is not limited to the engine and may be an electric motor or the like.

On the left side of the operator seat 8, a traveling lever 9L is provided. On the right side of the operator seat 8, a traveling lever 9R is provided. The traveling lever 9L disposed on the left is provided for operating the travel device 5A disposed on the left, and the traveling lever 9R disposed on the right is provided for operating the travel device 5B disposed on the right.

The working device 4 includes a boom 10, a bucket 11, a lift link 12, a control link 13, a boom cylinder (a hydraulic cylinder) 14 and a bucket cylinder 17. The boom 10 is provided on the side of the machine body 2. The bucket 11 is provided on a tip portion (a front end) of the boom 10. The lift link 12 and the control link 13 support a base portion (a rear portion) of the boom 10. The boom cylinder 14 moves the boom 10 upward and downward.

More specifically, the lift link 12, the control link 13, and the boom cylinder 14 a re provided on the side of the machine body 2. The upper portion of the lift link 12 is pivotally supported by the upper portion of the base portion of the boom 10. The lower portion of the lift link 12 is pivotally supported on the side portion of the rear portion of the machine body 2. The control link 13 is disposed forward from the lift link 12. One end of the control link 13 is pivotally supported by a lower portion of the base portion of the boom 10, and the other end is pivotally supported by the machine body 2.

The boom cylinder 14 is constituted of a hydraulic cylinder configured to move the boom 10 upward and downward. The upper portion of the boom cylinder 14 is pivotally supported by the front portion of the base portion of the boom 10. The lower portion of the boom cylinder 14 is pivotally supported by the side portion of the rear portion of the machine body 2. When the boom cylinder 14 is stretched and shortened, the boom 10 is swung up and down by the lift link 12 and the control link 13. The bucket cylinder 17 is constituted of a hydraulic cylinder configured to swing the bucket 11.

The bucket cylinder 17 couples the left portion of the bucket 11 and the boom disposed on the left to each other, and couples the right portion of the bucket 11 and the boom disposed on the right to each other. Meanwhile, it should be noted that, instead of the bucket 11, an auxiliary attachment such as a hydraulic crusher, a hydraulic breaker, an angle bloom, an auger, a pallet fork, a sweeper, a mower, a snow blower may be attached to the tip portion (the front portion) of the boom 10.

In the present embodiment, the traveling devices 5A and 5B respectively employ wheeled traveling devices 5A and 5B each having a front wheel 5F and a rear wheel 5R. Meanwhile, traveling devices 5A and 5B of a crawler type (including a semi-crawler type) may be employed as the traveling devices 5A and 5B.

Next, a working-system hydraulic circuit (a working-system hydraulic system) disposed in the skid steer loader 1 will be described below.

As shown in FIG. 1, the working-system hydraulic system is a system configured to operate the boom 10, the bucket 11, the auxiliary attachment, and the like. And, the working-system hydraulic system includes a control valve unit 70 and a hydraulic pump of working system (a first hydraulic pump) P1. In addition, the working-system hydraulic system includes a second hydraulic pump P2 different from the first hydraulic pump P1.

The first hydraulic pump P1 is a pump configured to be operated by the power of the prime mover 7, and is constituted of a gear pump of constant-displacement type (a constant-displacement type gear pump). The first hydraulic pump P1 is configured to output an operation fluid (a hydraulic oil) stored in a tank (an operation fluid tank) 15. The second hydraulic pump P2 is a pump configured to be operated by the power of the prime mover 7, and is constituted of a gear pump of constant-displacement type (a constant-displacement type gear pump). The second hydraulic pump P2 is configured to output the operation fluid stored in the tank (the operation fluid tank) 15.

Meanwhile, in the hydraulic system, the second hydraulic pump P2 is configured to output the hydraulic fluid for signals (a signal hydraulic fluid) and the hydraulic fluid for control (a control hydraulic fluid). Each of the hydraulic fluid for signals (the signal hydraulic fluid) and the hydraulic fluid for control (the control hydraulic fluid) is referred to as a pilot fluid (a pilot oil).

The control valve unit 70 includes a plurality of control valves 20. The plurality of control valves 20 are valves configured to control hydraulic actuators (hydraulic devices) of various types, the hydraulic actuators being disposed on the working machine 1. The hydraulic actuator is a device configured to be operated by the hydraulic fluid, for example, a hydraulic cylinder, a hydraulic motor, and the like. In the embodiment, the plurality of control valves 20 include a first control valve 20A, a second control valve 20B, and a third control valve 20C.

Firstly, the second control valve 20B and the third control valve 20C will be described below.

The second control valve 20B is a valve configured to control a hydraulic cylinder (a bucket cylinder) 17 that is configured to control the bucket 11. In other words, the second control valve 20B is a valve configured to control the bucket cylinder 17 that is a second hydraulic device configured to be operated by the hydraulic fluid. The third control valve 20C is a valve configured to control the hydraulic actuators (the hydraulic cylinder, the hydraulic motor, and the like) 16 mounted on the auxiliary attachment.

The second control valve 20B is a three-position switching valve having a spool directly acting with a pilot fluid (referred to as a pilot direct-acting spool type three-position switching valve). The second control valve 20B is configured to be switched to a neutral position 20 b 3, to a first position 20 b 1 other than the neutral position 20 b 3, and to a second position 20 b 2 other than the neutral position 20 b 3 and the first position 20 b 1. In the second control valve 20B, the switching between the neutral position 20 b 3, the first position 20 b 1, and the second position 20 b 2 is performed by a spool moved by operation of the operation member. A bucket cylinder 17 is connected to the second control valve 20B by a fluid tube.

Thus, when the second control valve 20B is set to the first position 20 b 1 by the operation of the operating member, the bucket cylinder 17 is shortened. When the bucket cylinder 17 is shortened, the bucket 11 performs a shoveling operation. When e second control valve 20B is set to the second position 20 b 2 by the operation of the operating member, the bucket cylinder 17 is stretched. When the bucket cylinder 17 is stretched, the bucket 11 performs a dumping operation.

Meanwhile, the switching of the second control valve 20B is performed by directly moving the spool with the operating member. However, the spool may be moved by the pressure of the operation fluid (the pilot fluid). The second control valve 20B is connected to the first control valve 20A by a central fluid tube 68 a. The second control valve 20B and the third control valve 20C are connected each other by a central fluid tube 68 b. When the second control valve 20B is in the neutral position 2083, the operation fluid supplied to the second control valve 20B is supplied to the third control valve 20C through the central fluid tube 68 b.

The third control valve 20C is a three-position switching valve having a spool directly acting with a pilot fluid (referred to as a pilot direct-acting spool type three-position switching valve). The third control valve 20C is configured to be switched to a neutral position 20C3, to a first position 20C1 other than the neutral position 20C3, and to a second position 20C2 other than the neutral position 20C3 and the first position 20C1. In the third control valve 20C, the switching between the neutral position 20C3, the first position 20C1, and the second position 20C2 is performed by a spool moved by a pressure of the pilot fluid.

A connecting member 18 is connected to the third control valve 20C through supply/discharge fluid tubes 83 a and 83 b. The supply/discharge fluid tubes 83 a and 83 b include a first fluid supply/discharge fluid tube 83 a and a second fluid supply/discharge fluid tube 83 b. A fluid tube connected to the hydraulic actuator 16 of the auxiliary attachment is connected to the connecting member 18.

Thus, when the third control valve 20C is set to the first position 20C1, the operation fluid can be supplied from the first fluid supply/discharge fluid tube 83 a to the hydraulic actuator 16 of the auxiliary attachment. When the third control valve 20C is set to the second position 20C2, the operation fluid can be supplied from the second fluid supply/discharge fluid tube 83 b to the hydraulic actuator 16 of the auxiliary attachment.

In this manner, when the operation fluid is supplied to the hydraulic actuator 16 from the supply/discharge fluid tube 83 a or the supply/discharge fluid tube 83 b, the hydraulic actuator 16 (the auxiliary attachment) can be operated. Meanwhile, when the third control valve 20C is in the neutral position 20C3, the hydraulic fluid supplied from the central fluid tube 68 b to the third control valve 20C is discharged from the central fluid tube 68 c connected to the third control valve 20C.

Next, the first control valve will be described below.

As shown in FIG. 1, the first control valve 20A is a valve configured to be applied to a series circuit. In the series circuit having a control valve on the upstream side (for example, the first control valve 20A) and a control valve on the downstream side (for example, the second control valve 20B), the operation fluid (a return fluid) returning from the hydraulic actuator to the first control valve 20A in the operation of the first control valve 20A flows to the second control valve 20B. The first control valve 20A is a valve configured to output a part of the return fluid to a fluid tube configured to discharge the operation fluid, the return fluid returning from the hydraulic actuator in the operation.

In the present embodiment, the first control valve 20A is connected by to a fluid tube a hydraulic cylinder (a boom cylinder) 14 that is one of the hydraulic actuators. In other words, the first control valve 20A is a valve configured to control the boom cylinder 14 that is the first hydraulic device configured to be activated by the hydraulic fluid. In addition, the first control valve 20A discharges the hydraulic fluid to a fourth fluid tube (a discharge fluid tube) 24 described later, the operation fluid returning from the boom cylinder 14.

The boom cylinder 14 includes a cylindrical body 14 a, a rod 14 b movably provided on the cylindrical body 14 a, and a piston 14 c provided on the rod 14 b. The boom cylinder 14 and the first control valve 20A are connected each other by communication tubes 21 and 22. The communication tubes 21 and 22 have a first fluid tube (a first communication tube) 21 and a second fluid tube (second communication tube) 22.

In other words, the first fluid tube (the first communication tube) 21 is a fluid tube in which the return fluid from the boom cylinder 14 flows, the return fluid being outputted at the time of shortening of the boom cylinder 14 that is the first hydraulic device. In addition, the second fluid tube (the second communication tube) 22 is a fluid tube in which the return fluid from the boom cylinder 14 flows, the return fluid being outputted at the time of stretching of the boom cylinder 14 that is the first hydraulic device. Each of the first fluid tube 21 and the second fluid tube 22 is configured to supply the operation fluid and is constituted of a tubular member such as a hydraulic hose, a pipe, a coupler, and a joint.

A first supply/discharge port 14 d for supplying and discharging the operation fluid is provided on a base end portion (on a side opposite to the rod 14 b side) of the cylindrical body 14 a. A second supply/discharge port 14 e for supplying and discharging the operation fluid is provided on a tip end portion (on the rod 14 b side) of the cylindrical body 14 a. When the boom cylinder 14 is shortened, the boom cylinder 14 discharges the operation fluid from the first supply/discharge port 14 d. When the boom cylinder 14 is stretched, the boom cylinder 14 discharges the operation fluid from the second supply/discharge port 14 e.

One end of the first fluid tube 21 is connected to the first supply/discharge port 14 d, and one end of the second fluid tube 22 is connected to the second supply/discharge port 14 e. That is, the second fluid tube 22 is a fluid tube connected to the boom cylinder 14 at a position different from the first fluid tube 21 that is connected to the boom cylinder 14.

As shown in FIG. 1, the first control valve 20A is a three-position switching valve having a spool directly acting with a pilot fluid (referred to as a pilot direct-acting spool type three-position switching valve). The first control valve 20A is configured to be switched to a neutral position 20 a 3, to a first position 20 a 1 other than the neutral position 20 a 3, and to a second position 20 a 2 other than the neutral position 20 a 3 and the first position 20 a 1.

The first control valve 20A has a plurality of ports. As shown in FIG. 1, the plurality of ports include a first port 31 (which may be referred to as a “first communication port”), a second port 32 (which may be referred to as a “second communication port”), a third port 33 (which may be referred to as a “input port”), a fourth port 34 (which may be referred to as a “discharge port”), and a fifth port 35 (which may be referred to as a “bypass port”).

The first port 31 is a port configured to be connected to the other d of the first fluid tube 21 that is connected to the boom cylinder 14. Thus, the operation fluid flowing from the first port 31 toward the boom cylinder 14 passes through the first fluid tube 21, and then enters the first supply/discharge port 14 d of the boom cylinder 14. In addition, the operation fluid flowing from the first supply/discharge port 14 d toward the first control valve 20A passes through the first fluid tube 21, and then enters the first port 31.

The second port 32 is a port configured to be connected to the other end of the second fluid tube 22 that is connected to the boom cylinder 14. Thus, the operation fluid flowing from the second port 32 toward the boom cylinder 14 passes through the second fluid tube 22, and then enters the second supply/discharge port 14 e of the boom cylinder 14. In addition, the operation fluid flowing from the second supply/discharge port 14 e toward the first control valve 20A passes through the second fluid tube 22, and then enters the second port 32.

The third port 33 is a port configured to be connected to a third fluid lube (a main fluid tube) 23 that is connected to the first hydraulic pump P1 configured to discharge the operation fluid. In particular, the third fluid tube 23 is branched into three tubes at the middle portion of the third fluid tube 23. And, a first branched fluid tube 23 a, a second branched fluid tube 23 b, and a third branched fluid tube 23 c are connected to the third port 33.

That is, the third or input port 33 includes a first input port 33 a connected to the first branched fluid tube 23 a, a second input port 33 b connected to the second branched fluid tube 23 b, and a central input port 33 c connected to the third branched fluid tube 23 c.

The fourth port 34 is a port configured to be connected to a fourth fluid tube (a discharge fluid tube) 24 that is connected to the operation fluid tank 15. In particular, the fourth fluid tube 24 includes a fluid tube 24 a. The fluid tube 24 a is a fluid tube configured to supply the operation fluid to the operation fluid tank 15, the operation fluid having passed through the first control valve 20A.

The discharge fluid tube 24 a includes a first discharge portion 24 a 1 connected to the first fluid tube 21, a second discharge portion 24 a 2 connected to the second fluid tube 22, a third discharge portion 24 a 3 connecting the first discharge portion 24 a 1 and the second discharge portion 24 a 2 to each other, and a fourth discharge portion 24 a 4 connecting e third discharge portion 24 a 3 and the operation fluid tank 15 to each other.

Here, the fluid tube including the third discharge portion 24 a 3 and the fourth discharge portion 24 a 4 may be respectively referred to as first discharge fluid tubes 24 a 3 and 24 a 4. In addition, the discharge fluid tube 24 includes a second discharge fluid tube 24 b. The second discharge fluid tube 24 b is a fluid tube branched from an output fluid tube 68 and configured to supply, to the fluid tube 24 a, the operation fluid having passed through the second control valve 20B and the operation fluid having passed through the third control valve 20C. The second discharge fluid tube 24 b is a fluid tube connected to the first discharge fluid tube 24 a 3.

A relief valve 27 is connected to the first discharge portion 24 a 1, and another relief valve 27 is connected to the second discharge portion 24 a 2. In addition, the first discharge portion 24 a 1 is provided with a bypass fluid tube, and the second discharge portion 24 a 2 is provided with a bypass fluid tube, the bypass fluid tubes connecting both sides of each of the relief valves 27 to each other. And, a check valve 29 is provided in the bypass fluid tube. The check valve 29 is a valve configured to allow the operation fluid to flow from the discharge fluid tube 24 side to the communication tubes (the first communication tube 21 and the second communication tube 22) and to block the operation fluid so as not to flow from the communication tubes to the discharge fluid tube 24 side.

The fourth discharge portion 24 a 4 is connected to the second discharge fluid tube 24 b. The third discharge portion 24 a 3 includes a connecting portion 26 a and branched discharging portions 26 b and 26 c. The connecting portion 26 a connects the first discharging portion 24 a 1 and the second discharging portion 24 a 2 to each other. The branched discharging portions 26 b and 26 c are branched from the connecting portion 26 a into at least two portions. The branched discharging portions 26 b and 26 c are connected to the fourth port 34 of the first control valve 20A.

That is, the fourth or discharge port 34 includes a port 34 a (which may be referred to as a “first discharge port”) and a port 34 b (which may be referred to as a “second discharge port”). The port 34 a is connected to the branched discharge portion 26 b, and the port 34 b is connected to the branched discharge portion 26 c. In the present embodiment, the fourth port 34 is a port including two ports 34 a and 34 b. However, the number of ports is not limited, and for example, the number of ports may be one.

The fifth port 35 is a port configured to discharge, to the outside, the operation fluid having passed through the first port 31 or the second port 32. That is, the fifth port 35 is a port configured to discharge, to a control valve on the downstream side (the second control valve 20B), the hydraulic fluid (the return fluid) returning from the boom cylinder 14 to the first port 31 or the hydraulic fluid (the returned fluid) returning from the boom cylinder 14 to the second port 32.

Now, the working-system hydraulic system is provided with a fifth fluid tube 25. The fifth fluid tube 25 is a fluid tube configured to supply the return fluid to the second control valve 20B when the first control valve 20A is in operation (when the spool 50 of the first control valve 20A moves).

In particular, when the first control valve 20A is in the first position 20 a 1, the first control valve 20A and the second control valve 20B are connected to each other by a fifth fluid tube (a supply fluid tube or a bypass fluid tube) 25. The fifth fluid tube 25 allows the return fluid to pass through the first control valve 20A, the return fluid returning from the first hydraulic actuator 14 to the first control valve 20A through the first fluid tube 21, and then supplies the return fluid to the second control valve 20B.

One end of the fifth fluid tube 25 is branched into two portions, and the first supply fluid tube 25 a (one of the two portions of the branched fluid tube) and the second supply fluid tube 25 b (the other one of the two portions of the branched fluid tube) are connected to the fifth port 35. That is, the fifth or bypass port 35 includes a port 35 a (which may be referred to as a “first bypass port”) and a port 35 b (which may be referred to as a “second bypass port”). The port 35 a is connected to the first supply fluid tube 25 a or the first bypass fluid tube. And, the port 35 b is connected to the second supply fluid tube 25 b or the second bypass fluid tube.

In the present embodiment, the fifth port 35 is a port including two ports 35 a and 35 b. However, the number of ports is not limited, and for example, the number of ports may be one.

In addition, when the first control valve 20A is in the second position 20 a 2, the first fluid tube 21 and the fifth fluid tube 25 are connected to each other by the first connection fluid tube 61 a. The first connection fluid tube 61 a is also referred to as a connection fluid tube. The first connection fluid tube 61 a is a fluid tube disposed on the first control valve 20A and is communicated with the first fluid tube 21.

In particular, the first connection fluid tube 61 a is a fluid tube configured to connect the first port 31 of the first control valve 20A to the fifth port 35 of the first control valve 20A when the first control valve 20A is set to the second position 20 a 2.

The working-system hydraulic system includes a branched fluid tube (a first branched fluid tube) 65 a that is branched from the first connection fluid tube 61 a and configured to discharge the return fluid. The first branched fluid tube 65 a is a fluid tube branched from the first connection fluid tube 61 a and configured to be communicated with the port 34 a when the first control valve 20A is in the second position 20 a 2. A throttle portion (a first throttle portion) 67 a is disposed on the first branched fluid tube 65 a, the throttle portion being configured to reduce a flow rate of the operation fluid.

The first throttle portion 67 a is constituted, for example, by making one portion of the first branched fluid tube 65 a narrower than the other portions of the first branched fluid tube 65 a. In other words, the first throttle portion 67 a is constituted by reducing a cross-sectional area of the one portion to be smaller than the other portion in the first branched fluid tube 65 a where the operation fluid flows. Meanwhile, the configuration of the first throttle portion 67 a is not limited to the example described above.

On the other hand, when the first control valve 20A is in the first position 20 a 1, the second fluid tube 22 and the fifth fluid tube 25 are connected to each other by the second internal fluid tube (a second connection fluid tube) 61 b. The second connection fluid tube 61 b is also referred to as a connection fluid tube. The second connection fluid tube 61 b is a fluid tube disposed on the first control valve 20A and communicated with the second fluid tube 22. The second connection fluid tube 61 b is a fluid tube configured to be connect the second port 32 of the first control valve 20A to the fifth port 35 of the first control valve 20A When the first control valve 20A is set to the first position 20 a 1.

Meanwhile, the working-system hydraulic system has a branched fluid tube (a second branched fluid tube) 65 b that is branched off from the second connection fluid tube 61 b and configured to discharge the return fluid. In particular, the second branched fluid tube 65 h is a fluid tube that is branched off from the second connection fluid tube 61 b and is configured to be communicated with the port 34 b when the first control valve 20A is in the first position 20 a 1. The second branched fluid tube 65 b is provided with a throttle portion (a second throttle portion) 67 b configured to reduce a flow rate of the operation fluid.

The second throttle portion 67 b is constituted, for example, by making one portion of the second branched fluid tube 65 b narrower than the other portions of the second branched fluid tube 65 b. In other words, the second throttle portion 67 b is constituted by reducing a cross-sectional area of the one portion to be smaller than the other portion in the second branched fluid tube 65 b where the operation fluid flows. Meanwhile, the configuration of the second throttle portion 67 h is not limited to the example described above.

In addition, the working-system hydraulic system has a setting portion configured to increase a pressure of the discharge fluid tube 24 connected to the first branched fluid tube 65 a or to the second branched fluid tube 65 b.

As shown in FIG. 1, the setting portion includes a check valve (a first check valve) 19 c and an oil cooler (a fluid cooler) 28, the check valve 19 c being constituted of an operation valve. The check valve 19 c is provided in the middle of the third discharge fluid tube 24 c that is communicated with the output fluid tube 68 (the central fluid tube 68 a, the central fluid tube 68 b, and the central fluid tube 68 c). The check valve 19 c is a valve configured to allow the hydraulic fluid to flow toward the hydraulic fluid tank 22 and to prevents the hydraulic fluid from flowing toward the discharge fluid tube 68. The check valve 19 c has a setting member 19 c 1 configured to set a differential pressure.

The setting member 19 c 1 is constituted of a spring or the like, and is configured to venerate a differential pressure by the valve body pushed with a predetermined biasing force from a side opposite to a direction allowing the flow of the hydraulic fluid (from a direction preventing the flow). The oil cooler 28 is provided in the middle of the first discharge fluid tubes 24 a 3 and 24 a 4 that are connected to the second discharge fluid tube 24 b. The hydraulic fluid discharged from the first discharge fluid tubes 24 a 3 and 24 a 4 flows into an inlet port 28 a of the oil cooler 28.

The discharge port 28 h, which is different from the inlet port 28 a of the oil cooler 28, is connected to the operation fluid tank 15. Here, paying attention to the second discharge fluid tube 24 b and the third discharge fluid tube 24 c provided with the check valve 19 c, the third discharge fluid tube 24 c and the second discharge fluid tube 24 b are connected to each other by the connecting portion 26. The check valve 19 c allows the hydraulic fluid to flow from the second discharge fluid tube 24 b toward the third discharge fluid tube 24 c, and blocks the operation fluid flowing from the third discharge fluid tube 24 c to the second discharge fluid tube 24 b.

Thus, in the section between the check valve 19 c and the connecting section 26 and in the section between the connecting section 26 and the inlet port 28 a of the oil cooler 28, the pressure of the hydraulic fluid is increased by the check valve 19 c serving as the setting portion. In this manner, when an amount of the operation fluid supplied to the fifth fluid tube (a supply fluid tube) 25 decreases, for example, the operation fluid in the second discharge fluid tube 24 b and the first discharge fluid tubes 24 a 3 and 24 a 4 can be supplied to the fifth fluid tube 25 through the branched fluid tubes 65 a and 65 b and the connection fluid tubes 61 a and 61 b.

For example, in the case where the boom cylinder 14 is stretched (the boom 10 is moved upward), the operation fluid (the return fluid) is supplied to the fifth fluid tube 25 through the second communication tube 22, the second port 32, and the second connection fluid tube 61 b.

Here, in the case where the bucket cylinder 17 is stretched (the bucket 11 is dumped) under the state where the boom 10 is moved upward, a relatively large amount of operation fluid is required. However, the operation fluid in the second discharge fluid tube 24 b and in the first discharge fluid tubes 24 a 3 and 24 a 4 can be supplied to the fifth fluid tube 25 through the branched fluid tube 65 b and the connection fluid tube 61 b. That is, it is possible to smoothly perform an operation of dumping the bucket 11 with the boom 10 being moved upward.

FIG. 2 shows a modified example of the setting portion. As shown in FIG. 2, the setting portion includes a throttle 67 d and a throttle 67 e, the throttle 67 d being provided in the fourth discharge portion 24 a 4, the throttle 67 e being provided in the third discharge fluid tube 24 c.

The hydraulic system of the working machine described above has the setting portions (a throttle 67 d and a throttle 67 e) configured to increase the pressures of the discharge fluid tubes (the branched discharge portions 26 b and 26 c of the first discharge fluid tube 24 a 3) that are communicated with the branched fluid tubes (the first branched fluid tube 65 a and the second branched fluid tube 65 b) branched from the connection fluid tubes (the first connection fluid tube 61 a and the second connection fluid tube 61 b).

In this manner, the pressure in the section between the ports 34 a and 34 b and the setting portion (the throttle 67 d and the throttle 67 e) can be increased in the branched discharge portions 26 b and 26 c. Thus, in the case where the operation fluid supplied to the fifth fluid tube (the supply fluid tube) 25 is for example reduced, it is possible to supply the hydraulic fluid of the branched discharge portions 26 b and 26 c to the fifth fluid tube through the branched fluid tubes 65 a and 65 b and the connection fluid tubes 61 a and 61 b.

In the embodiment described above, the branched fluid tubes 65 a and 65 b are provided respectively corresponding to the first position 20 a 1 and the second position 20 a 2 of the first control valve 20A. However, It is also possible to provide the branched fluid tube 65 b corresponding only to the first position 20 a 1 and to supply the operation fluid of the discharge fluid tube 24 to the branched fluid tube 65 b.

In addition, it is preferred that the setting portion is configured to increase a pressure in the discharge fluid tube 24, and the setting portion may be a relief valve provided in the fourth discharge portion 24 a 4 and the third discharge fluid tube 24 c.

In addition, in the present embodiment, the discharge fluid tube 24 has two fluid tubes, that is, the second discharge fluid tube 24 b and the third discharge fluid tube 24 c, However, when the second discharge fluid tube 24 b and the third discharge fluid tube 24 c are collectively constituted of a single fluid tube, the setting portion may be constituted of the oil cooler 28 and the check valve 19 c provided in the middle portion of the fluid tube.

Meanwhile, the setting portion may be the oil cooler 28, the check valve 19 c, a throttle, or a relief valve, or may be a combination thereof.

Meanwhile, a portion where the operation fluid flows of the second throttle portion 67 b has a cross-sectional area smaller than that of the first throttle portion 67 a. In other words, the second throttle portion 67 b through which the return fluid flows in the stretching of the boom cylinder 14 has a cross-sectional area smaller than that of the first throttle portion 67 a through which the return fluid flows when the boom cylinder 14 is shortened, at a portion through which the return fluid flows.

That is, the second throttle portion 67 b has a better throttle effect, and the first diaphragm 67 a has a throttle effect less than that of the second diaphragm 67 b. Thus, the flow rate of the hydraulic fluid supplied to the fifth fluid tube 25 under a condition where the first control valve 20A is set to the first position 20 a 1 can be substantially equivalent to the flow rate of the operation fluid supplied to the fifth fluid tube 25 under a condition where the first control valve 20A is set to the second position 20 a 2.

Orthogonal cross sections (the cross sections in a direction orthogonal to the rod 14) of the rod 14 b and the piston 14 c in the boom cylinder 14 will be considered below. Regarding the orthogonal cross sections, the cross-sectional area of the piston 14 c is larger than the cross-sectional area of the rod 14 b. Thus, when the boom cylinder 14 is shortened, an amount of the operation fluid discharged from the first supply/discharge port 14 d is larger than an amount of the operation fluid discharged when the boom cylinder 14 is stretched.

That is, when the boom cylinder 14 is shortened, the amount of the operation fluid returning to the first fluid tube 21 and the first port 31 (the amount of the return fluid) will be large. Conventionally, since the return fluid is supplied directly to the second control valve 20B, the operability of the hydraulic actuator (the bucket cylinder 17) operated by the second control valve 20B is lowered when the second control valve 20B is operated simultaneously with the first control valve 20A.

That is, the operation feeling is different when the first control valve 20A and the second control valve 20B are simultaneously operated from when the operation is not performed simultaneously. On the other hand, according to the first control valve 20A, since the cross-sectional area of the second throttle portion 67 b is smaller than the cross-sectional area of the first throttle portion 67 a, the operation feeling of the hydraulic actuator (the bucket cylinder 17) can be kept unchanged regardless of the stretching and shortening of the boom cylinder 14.

In particular, when the boom cylinder 14 is stretched (moving the boom 10 upward), the operation fluid (the return fluid) discharged from the second supply/discharge port 14 e will be less than the operation fluid (the return fluid) discharged from the first supply/discharge port 14 d due to the area ratio between the cross sections of the rod 14 b and the piston 14 c of the cylinder 14 (the cross section in the direction orthogonal to the rod 14).

In addition, when the bucket cylinder 17 is stretched (the bucket 11 is dumped), an external force is applied in a direction to stretch the bucket cylinder 17 due to the loading on the bucket 11 or the like. In this manner, the pressure in the fifth fluid tube 25 will be lower than that in the connection portion 26 and that in the inlet port 28 a, and thus the fluid in the third discharge portion 24 a 3 flows to the second branched fluid tube 65 b without returning to the tank 15.

Note that a configuration similar to the configuration of the first throttle portion 67 a and the second throttle portion 67 b in the present embodiment can also be applied to the second control valve 20B. In that case, the throttle portion through which the return fluid flows when the bucket cylinder 17 is stretched has a cross-sectional area smaller than that of the throttle portion through which the return fluid flows when the bucket cylinder 17 is shortened, in the portion through which the return fluid flows.

Second Embodiment

FIG. 3 shows a second embodiment of the control valve 20 according to the present invention. The control valve 20 of the second embodiment can be applied to the control valve 20 of the first embodiment described above. Meanwhile, the explanation of the configurations similar to the configurations of the first embodiment will be omitted. As shown in FIG. 3, the hydraulic system of the working machine is a system in which the first branched fluid tube 65 a, the second branched fluid tube 65 b, and the setting portion (the operation valve) are not included.

As shown in FIG. 4A, the first control valve 20A includes a main body B1. The main body B1 is formed of a casting, a resin, or the like. A fluid tube through which the operation fluid flows is formed inside the main body B1. That is, the main body B1 has a first internal fluid tube 41, a second internal fluid tube 42, a third internal fluid tube 43, a fourth internal fluid tube 44, and a fifth internal fluid tube 45.

In convenience of the explanation, the left side of the page in FIG. 4A to FIG. 4C is referred to as the left, the right side of the page is referred to as the right, the directions toward the left and toward the right are referred to as a lateral direction, and a direction orthogonal to the lateral direction is referred to as a vertical direction. In addition, the first internal fluid tube 41, the second internal fluid tube 42, the third internal fluid tube 43, the fourth internal fluid tube 44, and the fifth internal fluid tube 45 will be explained referring to a cross-sectional view of FIG. 4A.

The first internal fluid tube 41 is a fluid tube formed inside the main body B1, and is communicated with the first port 31. A first port 31 is provided on a left portion of the main body B1 in the lateral direction, and a first internal fluid tube 41 is formed next to the first port 31. The first internal fluid tube 41 is extended at least in the longitudinal direction.

The second internal fluid tube 42 is a fluid tube formed inside the main body B1, and is communicated with the second port 32. The second port 32 is provided on a right portion of the main body B1 in the lateral direction, and a second internal fluid tube 42 is formed next to the second port 32. The second internal fluid tube 42 is extended at least in the longitudinal direction.

The third internal fluid tube 43 is a fluid tube formed inside the main body B1, and is communicated with the third port 33. The third internal fluid tube 43 is formed in a central portion of the main body B1 in the lateral direction. In particular, the third internal fluid tube 43 includes a left fluid tube 43 a, a right fluid tube 43 b, and a central fluid tube 43 c.

The central fluid tube 43 c is formed at the center of the main body B1 in the lateral direction, and is communicated with the port 33 c. The left fluid tube 43 a is located on the left of the central fluid tube 43 c, and is communicated with the port 33 a. The right fluid tube 43 b is located on the right of the central fluid tube 43 c, and is communicated with the port 33 b. The left fluid tube 43 a and the central fluid tube 43 c are communicated with each other, and the right fluid tube 43 b and the central fluid tube 43 c are communicated with each other. The left fluid tube 43 a, the right fluid tube 43 b, and the central fluid tube 43 c are extended at least in the vertical direction.

The fourth internal fluid tube 44 is a fluid tube formed inside the main body B and is communicated with the fourth port 34. In particular, the fourth internal fluid tube 44 includes a left fluid tube 44 a and a right fluid tube 44 b.

The left fluid tube 44 a is formed on the left portion of the main body B1 in the lateral direction, and is communicated with the port 34 a. The left fluid tube 44 a is located on the left of the first internal fluid tube 41. The right fluid tube 44 b is formed on the right portion of the main body B1 in the lateral direction, and is communicated with the port 34 b. The right fluid tube 44 b is located on the right of the second internal fluid tube 42. The left fluid tube 44 a and the right fluid tube 44 b are extended at least in the vertical direction.

The fifth internal fluid tube 45 is a fluid tube formed inside the main body B1, and is communicated with the fifth port 35. In particular, the fifth internal fluid tube 45 includes a left fluid tube 45 a and a right fluid tube 45 b.

The left fluid tube 45 a is formed on the left portion of the main body B1 in the lateral direction, and is communicated with the port 35 a. The left fluid tube 45 a is located between the first internal fluid tube 41 and the left fluid tube 44 a of the fourth internal fluid tube 44. The right fluid tube 45 b is formed on the right portion of the main body B1 in the lateral direction, and is communicated with the port 35 b. The right fluid tube 45 b is located between the second internal fluid tube 42 and the right fluid tube 44 b of the fourth internal fluid tube 44. The left fluid tube 45 a and the right fluid tube 45 b are extended at least in the vertical direction.

Meanwhile, a wall portion 36 (a through hole 36 a) having an annular shape extending from one end (the left end) of the main body B1 to the other end (the right end) in the lateral direction is formed. That is, the main body B1 is formed with the through hole 36 a extending straight into which the spool 50 having a cylindrical shape is inserted.

The first internal fluid tube 41, the second internal fluid tube 42, the third internal fluid tube 43, the fourth internal fluid tube 44, and the fifth internal fluid tube 45 extend to the annular wall portion 36 constituting the through hole 36 a. The end portion 41 a of the first internal fluid tube 41 extends to the wall portion 36. The end portion 42 a of the second internal fluid tube 42 extends to the wall portion 36. The end portion 43 a 1 of the left fluid tube 43 a of the third internal fluid tube 43 extends to the wall portion 36. The end portion 43 b 1 of the right fluid tube 43 b of the third internal fluid tube 43 extends to the wall portion 36. The end portion 43 c 1 of the central fluid tube 43 c of the third internal fluid tube 43 extends to the wall portion 36.

The end portion 44 a 1 of the left fluid tube 44 a of the fourth internal fluid tube 44 extends to the wall portion 36. The end portion 44 b 1 of the right fluid tube 44 b of the fourth internal fluid tube 44 extends to the wall portion 36. The end portion 45 a 1 of the left fluid tube 45 a of the fifth internal fluid tube 45 extends to the wall portion 36. The end portion 45 b 1 of the right fluid tube 45 b of the fifth internal fluid tube 45 extends to the wall portion 36.

In addition, each of the end portion 41 a, the end portion 42 a, the end portion 43 a 1, the end portion 43 b 1, the end portion 43 c 1, the end portion 44 a 1, the end portion 44 b 1, the end portion 45 a 1, and the end portion 45 b 1 is formed in a concave shape.

As shown in FIG. 4A, the first control valve 20A has a spool 50. The spool 50 is configured to move inside the main body B1 to change the communication destinations of the first internal fluid tube 41, the second internal fluid tube 42, the third internal fluid tube 43, the fourth internal fluid tube 44 and the fifth internal fluid tube 45.

Hereinafter, the spool 50 will be described below in detail.

The spool 50 is formed to have a cylindrical shape. The spool 50 having a cylindrical shape is inserted into the through hole 36 a formed inside the main body B1. The left end or the right end of the spool 50 protrudes from the main body B1. An operation member such as a lever is connected to the protruding portion (the projecting portion) of the spool 50.

The spool 50 has a first communicating portion 51. The first communicating portion 51 is a portion configured to communicate the second internal fluid tube 42, the fourth internal fluid tube 44, and the fifth internal fluid tube 45 with each other. In particular, the first communicating portion 51 includes a first extending fluid tube 51 a, the plurality of second extending fluid tubes 51 b, a plurality of third extending fluid tubes 51 c, and a first concaved portion 51 d.

The first extending fluid tube 51 a is a fluid tube extending inside the spool 50 in the longitudinal direction (an axial direction) of the spool 50, and is formed by forming inside the spool 50 a hole extending in the axial direction of the spool 50. The first extending fluid tube 51 a extends from the middle portion of the spool 50 to the right portion. The left end and the right end of the first extending fluid tube 51 a are closed. Accordingly, the hydraulic fluid that has entered the first extending fluid tube 51 a flows inside the spool 50 in the axial direction of the spool 50.

The plurality of second extending fluid tubes 51 b is a fluid tube extending from the left end of the first extending fluid tube 51 a to the outer circumference surface of the spool 50, and is communicated with the first extending fluid tube 51 a. The plurality of second extending fluid tubes 51 b are communicated with the left portion of the first extending fluid tube 51 a. As shown in FIG. 4A, the spool 50 is provided with the plurality of second extending fluid tubes 51 b at a predetermined interval in the circumferential direction.

The plurality of third extending fluid tubes 51 c are fluid tubes extending from the middle of the first extending fluid tube 51 a to the outer circumference face of the spool 50, and is communicated with the first extending fluid tube 51 a. The plurality of third extending fluid tubes 51 c are communicated with a middle portion of the first extending fluid tube 51 a. As shown in FIG. 4A, the spool 50 is provided with the plurality of third extending fluid tubes 51 c at a predetermined interval in the circumferential direction.

The first concave portion 51 d is a portion formed by annularly denting the outer circumference surface of the spool 50. The first concave portion 51 d is located on the right portion of the spool 50 and is overlapped with the second extending fluid tube 51 b.

Meanwhile, the spool 50 has the second communicating portion 52.

The second communicating portion 52 is configured to communicate the first internal fluid tube 41 and the fifth internal fluid tube 45 with each other. In addition, the second communicating portion 52 is configured to communicate the first internal fluid tube 41 and the third internal fluid tube 43 with each other. In particular, the second communicating portion 52 includes the second concave portion 52 a. The second concave portion 52 a is a portion formed by annularly denting the outer circumference surface of the spool 50. The second recessed portion 52 a is located on the left portion of the spool 50.

As shown in FIG. 4B, the spool 50 is positioned in the middle portion (the middle position 20 a 4) between the neutral position 20 a 3 and the first position 20 a 1. To be explained in detail, the first concave portion 51 d and the end portion 42 a of the second internal fluid tube 42 are overlapped (matched) with each other.

In addition, the third extending fluid tube 51 c is overlapped (matched) with the right fluid tube 44 b (the end portion 44 b 1) of the fourth internal fluid tube 44. That is, when the first control valve 20A is in the middle position 20 a 4, the second internal fluid tube 42 and the fourth internal fluid tube 44 can be communicated with each other.

When the first control valve 20A is in the middle position 20 a 4, the return fluid returning from the boom cylinder (the first hydraulic device) 14 to the first control valve 20A is discharged through the second fluid tube 22, the second internal fluid tube 42, the first concave portion 51 d, the first communicating portion 51, the fourth internal fluid tube 44, and the fourth fluid tube 24, as indicated by R1 in FIG. 4B.

As shown in FIG. 4C, the spool 50 is located at the first position 20 a 1 (the communicating position 20 a 1). To be explained in detail, the first concave portion 51 d, the end portion 42 a of the second internal fluid tube 42, and the right fluid tube 45 b (the end portion 45 b 1) of the fifth internal fluid tube 45 are overlapped (matched) with each other. In addition, the third extending fluid tube 51 c and the right fluid tube 44 b (the end portion 44 b 1) of the fourth internal fluid tube 44 are overlapped (matched) with each other.

The second concave portion 52 a, the end portion 41 a of the first internal fluid tube 41, and the left fluid tube 43 a (the end portion 43 a 1) of the third internal fluid tube 43 are overlapped (matched) with each other. That is, when the first control valve 20A is in the first position 20 a 1, the second internal fluid tube 42, the fourth internal fluid tube 44, and the fifth internal fluid tube 45 can communicate with each other.

When the first control valve 20A is in the first position 20 a 1, the return fluid returning from the boom cylinder 14 to the first control valve 20A is discharged through the second internal fluid tube 42, the first communicating portion 51, and the fourth internal fluid tube 44, as indicated by R2 in FIG. 4C. In addition, the return fluid returning from the boom cylinder 14 to the first control valve 20A is supplied to the second control valve 20B through the second fluid tube 22, the second internal fluid tube 42, the first communicating portion 51, the fifth internal fluid tube 45, and the fifth fluid tube 25.

When the first control valve 20A is in the first position 20 a 1, the hydraulic fluid discharged from the operation fluid tank P1 is supplied to the boom cylinder 14 through the third internal fluid tube 43 (the right fluid tube 43 a), the second internal fluid tube 42, the second communicating portion 52, the first internal fluid tube 41 (the end portion 41 a), and the first fluid tube 21, as indicated by R3 in FIG. 4C.

As described above, when the spool 50 is in the middle position 20 a 4, the spool 50 has the first communicating portion 51 configured to communicate the second internal fluid tube 42 and the fourth internal fluid tube 44 with each other. In this manner, in the case where the spool 50 is moved from the neutral position 20 a 3 to the first position 20 a 1, the second internal fluid tube 42 and the fourth internal fluid tube 44 can be communicated with each other before the second internal fluid tube 42 and the fifth internal fluid tube 45 are communicated with each other. In addition, in the case where the spool 50 is moved from the neutral position 20 a 3 to the first position 20 a 1, the second internal fluid tube 42 and the fourth internal fluid tube 44 can be communicated with each other before the first internal fluid tube 41 and the third internal fluid tube 43 are communicated with each other.

For example, when paying attention to the control valve (the first control valve 20A) on the upstream side and the control valve (the second control valve 20B) on the downstream side, the second internal fluid tube 42 and the fourth internal fluid tube 44 can be communicated with each other before the second internal fluid tube 42 and the fifth internal fluid tube 45 are communicated with each other. Thus, the operation fluid having passed through the control valve (the first control valve 20A) on the upstream side can be discharged independently from the control valve (the second control valve 20B) on the downstream side, and thus it is possible to stably operate the first hydraulic equipment 14 disposed on the upstream side.

In addition, the spool 50 has a first communicating portion 51 configured to communicate the second internal fluid tube 42, the fourth internal fluid tube 44, and the fifth internal fluid tube 45 with each other. The first communicating portion 51 includes a first extending fluid tube 51 a, a plurality of second extending fluid tubes 51 b, and a plurality of third extending fluid tubes 51 c. The first extending fluid tube 51 a extends in the longitudinal direction of the spool 50. The plurality of second extending fluid tubes 51 b extends from one end of the first extending fluid tube 51 a to the outer circumference surface of the spool 50. The plurality of third extending fluid tubes 51 c extends from a middle portion of the first extending fluid tube 51 a to the outer circumference surface of the spool 50.

In this manner, the first communicating section 51 can be provided by forming the first extending fluid tube 51 a, the second extending fluid tube 51 b, and the third extending fluid tube 51 c in the inside of and on the outer circumference surface of the spool 50. Thus, the operation fluid can be discharged by the first communicating portion 51 without processing the main body B1, the first communicating portion 51 being provided in the spool 50.

Meanwhile, the configurations similar to the configurations of the first communicating portion 51 can also be applied to the left portion of the spool 50. That is, when the configuration similar to the first position 20 a 1 is applied to the second position 20 a 2, the first internal fluid tube 41 and the fourth internal fluid tube 44 are communicated with each other before the first internal fluid tube 41 and the fifth internal fluid tube 45 are communicated with each other in the case where the spool 50 is moved from the neutral position 20 a 3 to the second position 20 a 2.

In addition, in the case where the spool 50 is moved from the neutral position 20 a 3 to the second position 20 a 2, the first internal fluid tube 41 and the fourth internal fluid tube 44 can be communicated with each other before the second internal fluid tube 42 and the third internal fluid tube 43 are communicated with each other.

In the above description, the embodiment of the present invention has been explained. However, all the features of the embodiments disclosed in this application should be considered just as examples, and the embodiments do not restrict the present invention accordingly. A scope of the present invention is shown not in the above-described embodiments but in claims, and is intended to include all modifications within and equivalent to a scope of the claims.

In the above-described embodiment, the first hydraulic device is the boom cylinder 14, and the second hydraulic device is the bucket cylinder 17. However, the first hydraulic device and the second hydraulic device may be other hydraulic cylinders and are not limited to the configurations. In addition, although the discharge fluid tube 24 is connected to the operation fluid tank 15, the discharge destination of the operation fluid is not limited to the operation fluid tank 15, may be a suction portion of the hydraulic pump, and may be another component, and is not limited to the configurations.

Third Embodiment

Referring to the drawings appropriately, preferred embodiments of the hydraulic system of the working machine according to the present invention and preferred embodiments of the working machine provided with the hydraulic system will be described below.

Firstly, the working machine will be explained.

FIG. 6 shows a side view of the working machine according to the embodiment of the present invention. FIG. 6 shows a skid steer loader as an example of the working machine. However, the working machine according to the embodiment is not limited to the skid steer loader, and may be another type of a loader working machine such as a compact track loader. In addition, a working machine other than the loader working machine may be employed.

The working machine 1 includes the machine body (a vehicle body) 2, the cabin 3, the working device 4, and the traveling devices 5A and 5B.

The cabin 3 is mounted on the machine body 2. An operator seat 8 is disposed at a rear portion of an inside of the cabin 3. In explanations of the embodiments of the present invention, a front side (a left side in FIG. 6) of the operator seated on the operator seat 8 of the working machine 1 is referred to as the front (a front side), a rear side (a right side in FIG. 6) of the operator seated on the operator seat 8 of the working machine 1 is referred to as the rear (a rear side), a left side (a front surface side in FIG. 6) of the operator seated on the operator seat 8 of the working machine 1 is referred to as the left (a left side), and a right side (a back surface side in FIG. 6) of the operator seated on the operator seat 8 of the working machine 1 is referred to as the right (a right side).

In addition, a horizontal direction corresponding to a direction perpendicular to the front-to-rear direction will be referred to as a machine width direction. A direction extending from the center portion of the machine body 2 to the right portion or the left portion will be referred to as machine outward. In other words, the machine outward is a machine width direction that corresponds to a direction separating away from the machine body 2. In the explanation, a direction opposite to the machine outward is referred to as a machine inward. In other words, the machine inward is a machine width direction that corresponds to a direction approaching the machine body 2.

The cabin 3 is mounted on the machine body 2. The working device 4 is a device configured to perform a work, and is mounted on the machine body 2. The traveling device 5A is a device configured to allow the machine body 2 to travel, and is disposed on the left side of the machine body 2. The traveling device 5B is a device configured to allow the machine body 2 to travel, and is disposed on the right side of the machine body 2. A prime mover (a motor) 7 is disposed at a rear portion of an inside of the machine body 2. The prune mover 7 is a diesel engine (an engine). Meanwhile, it should be noted that the prime mover 7 is not limited to the engine and may be an electric motor or the like.

On the left side of the operator seat 8, a traveling lever 9L is provided. On the right side of the operator seat 8, a traveling lever 9R is provided. The traveling lever 9L disposed on the left is provided for operating the travel device 5A disposed on the left, and the traveling lever 9R disposed on the right is provided for operating the travel device 5B disposed on the right.

The working device 4 includes a boom 10, a bucket 11, a lift link 12, a control link 13, a boom cylinder (a hydraulic cylinder) 14 and a bucket cylinder 17. The boom 10 is provided on the side of the machine body 2. The bucket 11 is provided on a tip portion (a front end) of the boom 10. The lift link 12 and the control link 13 support a base portion (a rear portion) of the boom 10. The boom cylinder 14 moves the boom 10 upward and downward.

More specifically, the lift link 12, the control link 13, and the boom cylinder 14 are provided on the side of the machine body 2. The upper portion of the lift link 12 is pivotally supported by the upper portion of the base portion of the boom 10. The lower portion of the lift link 12 is pivotally supported on the side portion of the rear portion of the machine body 2. The control link 13 is disposed forward from the lift link 12. One end of the control link 13 is pivotally supported by a lower portion of the base portion of the boom 10, and the other end is pivotally supported by the machine body 2.

The boom cylinder 14 is constituted of a hydraulic cylinder configured to move the boom 10 upward and downward. The upper portion of the boom cylinder 14 is pivotally supported by the front portion of the base portion of the boom 10. The lower portion of the boom cylinder 14 is pivotally supported by the side portion of the rear portion of the machine body 2. When the boom cylinder 14 is stretched and shortened, the boom 10 is swung up and down by the lift link 12 and the control link 13. The bucket cylinder 17 is constituted of a hydraulic cylinder configured to swing the bucket 11.

The bucket cylinder 17 couples the left portion of the bucket 11 and the boom disposed on the left to each other, and couples the right portion of the bucket 11 and the boom disposed on the right to each other. Meanwhile, it should be noted that, instead of the bucket 11, an auxiliary attachment such as a hydraulic crusher, a hydraulic breaker, an angle bloom, an auger, a pallet fork, a sweeper, a mower, a snow blower may be attached to the tip portion (the front portion) of the boom 10.

In the present embodiment, the traveling devices 5A and 5B respectively employ wheeled traveling devices 5A and 5B each having a front wheel 5F and a rear wheel 5R. Meanwhile, traveling devices 5A and 5B of a crawler type (including a semi-crawler type) may be employed as the traveling devices 5A and 5B.

Next, a working-system hydraulic circuit (a working-system hydraulic system) disposed in the skid steer loader 1 will be described below.

As shown in FIG. 5, the working-system hydraulic system is a system configured to operate the boom 10, the bucket 11, the auxiliary attachment, and the like. And, the working-system hydraulic system includes a control valve unit 70 and a hydraulic pump of working system (a first hydraulic pump) P1. In addition, the working-system hydraulic system includes a second hydraulic pump P2 different from the first hydraulic pump P1.

The first hydraulic pump P1 is a pump configured to be operated by the power of the prime mover 7, and is constituted of a gear pump of constant-displacement type (a constant-displacement type gear pump). The first hydraulic pump P1 is configured to output an operation fluid (a hydraulic oil) stored in a tank (an operation fluid tank) 15. The second hydraulic pump P2 is a pump configured to be operated by the power of the prime mover 7, and is constituted of a gear pump of constant-displacement type (a constant-displacement type gear pump).

The second hydraulic pump P2 is configured to output the operation fluid stored in the tank (the operation fluid tank) 15. Meanwhile, in the hydraulic system, the second hydraulic pump P2 is configured to output the hydraulic fluid for signals (a signal hydraulic fluid) and the hydraulic fluid for control (a control hydraulic fluid). Each of the hydraulic fluid for signals (the signal hydraulic fluid) and the hydraulic fluid for control (the control hydraulic fluid) is referred to as a pilot fluid (a pilot oil).

The plurality of control valves 20 are valves configured to control various types of the hydraulic actuators disposed on the working machine 1. The hydraulic actuator is a device configured to be operated by the hydraulic fluid, such as a hydraulic cylinder, a hydraulic motor, or the like. In the embodiment, the plurality of control valves 20 include a boom control valve 20A, a bucket control valve 20B, and a auxiliary control valve 20C.

The boom control valve 20A is a valve configured to control the hydraulic actuator (the boom cylinder) 14 that is configured to operate the boom 10. The boom control valve 20A is a three-position switching valve having a spool directly acting with a pilot fluid (referred to as a pilot direct-acting spool type three-position switching valve). The boom control valve 20A is configured to be switched to a neutral position 20 a 3, to a first position 20 a 1 other than the neutral position 20 a 3, and to a second position 20 a 2 other than the neutral position 20 a 3 and the first position 20 a 1. In the boom control valve 20A, the switching between the neutral position 20 a 3, the first position 20 a 1, and the second position 20 a 2 is performed by a spool moved by operation of the operation member.

The switching of the boom control valve 20A is performed by directly moving the spool with manual operation of the operating member. However, the spool may be moved by the hydraulic operation (by the hydraulic operation using a pilot valve, the hydraulic operation using a proportional valve), the spool may be moved by the electric operation (the electric operation by magnetizing the solenoid), or the spool may be moved by other methods.

The boom control valve 20A and the first hydraulic pump P1 are connected to each other by an output fluid tube 27. A discharge fluid tube 24 a connected to the operation fluid tank 15 is connected to a section of the output fluid tube 27 between the boom control valve 20A and the first hydraulic pump P1. A relief valve (a main relief valve) 25 is disposed on a middle portion of the discharge fluid tube 24 a.

The hydraulic fluid discharged from the first hydraulic pump P1 passes through the output fluid tube 27 and is supplied to the boom control valve 20A. In addition, the boom control valve 20A and the boom cylinder 14 are connected to each other by a fluid tube 21.

In particular, the boom cylinder 14 includes a cylindrical body 14 a, a rod 14 b movably provided on the cylindrical body 14 a, and a piston 14 c provided on the rod 14 b. A first port 14 d for supplying and discharging the operation fluid is provided on a base end portion (on a side opposite to the rod 145 side) of the cylindrical body 14 a. A second port 14 e for supplying and discharging the operation fluid is provided on a tip end (on the rod 14 b side) of the cylindrical body 14 a.

The fluid tube 21 has a first connection fluid tube 21 a and a second connection fluid tube 21 b. The first connection fluid tube 21 a connects the first port 31 of the boom control valve 20A to the first port 14 d of the boom cylinder 14. The second connection fluid tube 21 b connects the second port 32 of the boom control valve 20A to the second port 14 e of the boom cylinder 14.

Thus, when the boom control valve 20A is set to the first position 20 a 1, the operation fluid can be supplied from the first connection fluid tube 21 a to the first port 14 d of the boom cylinder 14, and the operation fluid can be discharged from the second port 14 e of the boom cylinder 14 to the second connection fluid tube 21 b.

In this manner, the boom cylinder 14 is stretched, and thereby the boom 10 moves upward. When the boom control valve 20A is set to the second position 20 a 2, it is possible to supply the operation fluid from the second connection fluid tube 21 b to the second port 14 e of the boom cylinder 14, and possible to discharge the operation fluid from the first port 14 d of the boom cylinder 14 to the first connection fluid tube 21 a. In this manner, the boom cylinder 14 is shortened, and thereby the boom 10 moves downward.

The bucket control valve 20B is a valve configured to control the hydraulic cylinder (the bucket cylinder) 17 that is configured to control the bucket 11. The bucket control valve 20B is a three-position switching valve having a spool directly acting with a pilot fluid (referred to as a pilot direct-acting spool type three-position switching valve).

The bucket control valve 20B is configured to be switched to a neutral position 20 b 3, to a first position 20 b 1 other than the neutral position 20 b 3, and to a second position 20 b 2 other than the neutral position 20 b 3 and the first position 20 b 1. In the second control valve 20B, the switching between the neutral position 20 b 3, the first position 20 b 1, and the second position 20 b 2 is performed by a spool moved by operation of the operation member.

The switching of the bucket control valve 20B is performed by directly moving the spool with manual operation of the operating member. However, the spool may be moved by the hydraulic operation (by the hydraulic operation using a pilot valve, the hydraulic operation using a proportional valve), the spool may be moved by the electric operation (the electric operation by magnetizing the solenoid), or the spool may be moved by other methods.

The bucket control valve 208 and the bucket cylinder 17 are connected to each other by a fluid tube 22. In particular, the bucket cylinder 17 includes a cylindrical body 17 a, a rod 17 b movably provided on the cylindrical body 17 a, and a piston 17 c provided on the rod 17 b. A first port 17 d configured to supply and discharge the operation fluid is provided at the base end portion (on a side opposite to the rod 17 b side) of the cylindrical body 17 a. A second port 17 e configured to supply and discharge the operation fluid is provided on the tip end side (on the rod 17 b) of the cylindrical body 17 a.

The fluid tube 22 has a first connection fluid tube 22 a and a second connection fluid tube 22 a. The first connection fluid tube 22 a connects the first port 35 of the bucket control valve 20B to the second port 17 e of the bucket cylinder 17. The second connection fluid tube 22 a connects the second port 36 of the bucket control valve 20B to the first port 17 d of the bucket cylinder 17.

Thus, when the bucket control valve 20B is set to the first position 20B1, the operation fluid can be supplied from the first connection fluid tube 22 a to the second port 17 e of the bucket cylinder 17, and the operation fluid can be discharged from the first port 17 d of the bucket cylinder 17 to the second supply tube 22 b.

In this manner, the bucket cylinder 17 is shortened, and thus the bucket 11 is operated in a shoveling manner. When the bucket control valve 20B is set to the second position 20 a 2, the hydraulic fluid can be supplied from the second supply tube 22 b to the first port 17 d of the bucket cylinder 17, and the hydraulic fluid can be discharged from the second port 17 e of the bucket cylinder 17 to the first connection fluid tube 22 a. In this manner; the bucket cylinder 17 is stretched, and thus the bucket 11 is operated in the dumping manner.

Meanwhile, a discharge fluid tube 24 c is connected to the first connection fluid tube 22 a and the second connection fluid tube 22 b, and a relief valve 38 is provided on the discharge fluid tube 24 c. A set pressure of the relief valve 38 is determined, for example, to be higher than a set pressure of the main relief valve 25.

The auxiliary control valve 20C is a three-position switching valve having a spool directly acting with a pilot fluid (referred to as a pilot direct-acting spool type three-position switching valve). The auxiliary control valve 20C is configured to be switched to a neutral position 20 c 3, to a first position 20 c 1 other than the neutral position 20 c 3, and to a second position 20 c 2 other than the neutral position 20 c 3 and the first position 20 c 1.

In the auxiliary control valve 20C, the switching between the neutral position 20 c 3, the first position 20 c 1, and the second position 20 c 2 is performed by a spool moved by operation of the operation member. A connecting member 18 is connected to the auxiliary control valve 20C by the supply/discharge fluid tubes 83 a and 83 b. A fluid tube connected to the hydraulic actuator 16 of the auxiliary attachment is connected to the connecting member 18.

Thus, when the auxiliary control valve 20C is set to the first position 20 c 1, the operation fluid can be supplied from the supply/discharge fluid tube 83 a to the hydraulic actuator 16 of the auxiliary attachment. When the auxiliary control valve 20C is set to the second position 20 c 2, the operation fluid can be supplied from the supply/discharge fluid tube 83 b to the hydraulic actuator 16 of the auxiliary attachment.

In this manner, when the operation fluid is supplied from the supply/discharge fluid tube 83 a or the supply/discharge fluid tube 83 b to the hydraulic actuator 16, the hydraulic actuator 16 (the auxiliary attachment) can be operated.

Meanwhile, in the hydraulic system, a series circuit (a series fluid tube) is employed. In the series circuit, the hydraulic fluid having returned from the hydraulic actuator to the control valve on the upstream side can be supplied to the control valve disposed on the downstream side. For example, paying attention to the bucket control valve 20B and the auxiliary control valve 20C, the bucket control valve 20B is the control valve disposed on the upstream side, and the auxiliary control valve 20C is the control valve disposed on the downstream side.

Hereinafter, the control valve on the upstream side is referred to as “a first control valve”, and the control valve on the downstream side is referred to as “a second control valve”. A control valve other than the first control valve and the second control valve, the control valve being provided on the upstream side of the second control valve is referred to as “a third control valve”.

In addition, the hydraulic actuator corresponding to the first control valve is referred to as “a first hydraulic actuator”, the hydraulic actuator corresponding to the second control valve is referred to as “a second hydraulic actuator”, and the hydraulic actuator corresponding to the third control valve is referred to as “a third hydraulic actuator”. The fluid tube configured to supply the return fluid, which is the operation fluid returning from the first hydraulic actuator to the first control valve, to the second control valve is referred to as “a first fluid tube”.

In the embodiment, the bucket control valve 20B is referred to as “the first control valve”, the auxiliary control valve 20C is referred to as “the second control valve”, and the boom control valve 20A is referred to as “the third control valve”. In addition, the bucket cylinder 17 is referred to as “the first hydraulic actuator”, the hydraulic actuator 16 of the auxiliary attachment is referred to as “the second hydraulic actuator”, and the boom cylinder 14 is referred to as “the third hydraulic actuator”.

Hereinafter, the first control valve, the second control valve, and the third control valve will be described below in detail.

The third control valve 20A and the output portion of the first hydraulic pump P1 are connected to each other by an output fluid tube 27. The output fluid tube 27 is branched off at a middle portion 47 a. The branched fluid tube of the output fluid tube 27 is connected to the first input port 46 a and the second input port 46 b of the third control valve 20A. In addition, the output fluid tube 27 is connected to the third input port 46 c of the third control valve 20A.

In this manner, the hydraulic fluid outputted from the first hydraulic pump P1 can be supplied into the third control valve 20A through the output fluid tube 27, the first input port 46 a, the second input port 46 b, and the third input port 46 c. The third control valve 20A and the first control valve 20B are connected to each other by a central fluid tube 51. The central fluid tube 51 connects the third output port 41 c of the third control valve 20A to the third input port 42 c of the first control valve 20B.

Meanwhile, when the third control valve 20A is set to the neutral position 20 a 3, the central fluid tube 53 c connecting the third input port 46 c to the third output port 41 c is communicated through therein, and thereby the supplied fluid that is the operation fluid supplied from the output fluid tube 27 to the third control valve 20A passes through the third control valve 20A and then is supplied to the central fluid tube 51.

The third control valve 20A and the first control valve 20B are connected to each other by a return fluid tube 61 separately from the central fluid tube 51. The return fluid tube 61 is a fluid tube configured to supply the return fluid to the first control valve 20B through the third control valve 20A, the return fluid returning from the third hydraulic actuator 14 to the third control valve 20A. For convenience of the explanation, the return fluid tube 61 may be referred to as “a fourth fluid tube”.

The return fluid tube 61 has a second connection fluid tube 21 b, an internal fluid tube 61 a, and an external fluid tube 61 b. The second connection fluid tube 21 b is a fluid tube connecting the second port 32 of the third control valve 20A to the second port 14 e of the third hydraulic actuator 14, and also id a fluid tube in which the return fluid discharged from the second port 14 e of the third hydraulic actuator 14 flows.

The second connection fluid tube 21 b is connected to the discharge fluid tube 24 b. The discharge fluid tube 24 b includes a fluid tube 24 b 1, a fluid tube 24 b 2, and a fluid tube 24 b 3. The fluid tube 24 b 1 is connected to the second connection fluid tube 21 b, the fluid tube 24 b 2 is connected to the first discharge port 33 a and the second discharge port 33 b of the third control valve 20A, and the fluid tube 24 b 3 connects the operation fluid tank 15 to a confluent portion of the fluid tube 24 b 1 and the passage 24 b 2. A relief valve 37 is provided at the middle of the fluid tube 24 b 1. The set pressure of the relief valve 37 is set, for example, to be higher than the set pressure of the main relief valve 25.

The internal fluid tube 61 a is a fluid tube disposed on the third control valve 20A and communicated with the second connection fluid tube 21 b. In particular, when the third control valve 20A is set to the second position 20 a 2, the internal fluid tube 61 a is a fluid tube connecting the second port 32 of the third control valve 20A to the first output port 41 a of the third control valve 20A.

The external fluid tube 61 b is a fluid tube communicated with the internal fluid tube 61 a and connected to the first control valve 20B. The external fluid tube 61 b connects the first output port 41 a of the third control valve 20A to the first input port 42 a of the first control valve 20B, and connects the second output port 41 b of the third control valve 20A to the second input port 42 b of the first control valve 20B. The middle portion of the external fluid tube 61 b is connected to the central fluid tube 51.

In other words, the external fluid tube 61 b and the central fluid tube 51 are connected to each other at a middle portion. In the external fluid tube 61 b, a check valve 29 a is provided between a connecting portion 63 where the external fluid tube 61 b and the central fluid tube 51 are connected to each other and the first control valve 20B. The check valve 29 a allows the hydraulic fluid to flow from the connecting portion 63 to the first control valve 20B, and prevents the hydraulic fluid from flowing from the first control valve 20B to the connecting portion 63.

In addition, in the external fluid tube 61 b, a check valve 64 is provided between the connecting portion 63 and the third control valve 20A. The check valve 64 allows the hydraulic fluid to flow from the third control valve 20A to the connecting portion 63, and prevents the hydraulic fluid from flowing from the connecting portion 63 to the third control valve 20A.

The first control valve 20B and the second control valve 20C are connected to each other by a central fluid tube (a second fluid tube) 72. The central fluid tube 72 connects the third output port 43 c of the first control valve 20B to the third input port 44 c of the second control valve 20C.

Thus, when the first control valve 20B is set to the neutral position 20 b 3, the supply fluid that is the operation fluid supplied to the first control valve 20B passes through a central fluid tube 73 c connecting the third input port 42 c to the third output port 43 c, and then is supplied to the central fluid tube 72 connected to the third output port 43 c.

The first control valve 20B and the second control valve 20C are connected to each other by the first fluid tube 81 separately from the central fluid tube 72. The first fluid tube 81 is a fluid tube configured to supply the return fluid to the second control valve 20C through the first control valve 20B, the return fluid returning from the first hydraulic actuator 17 to the first control valve 20B.

The first fluid tube 81 has a fluid tube (a first connection fluid tube) 22 a, an internal fluid tube 81 a, and an external fluid tube 81 b. The first connection fluid tube 22 a is a fluid tube connecting the first port 35 of the first control valve 20B to the second port 17 e of the first hydraulic actuator 17, and is a fluid tube in which the return fluid discharged from the second port 17 e flows.

Meanwhile, the fluid tube (the second connection fluid tube) 22 b is connected to the discharge fluid tube 24 b. The discharge fluid tube 24 b has a fluid tube 24 b 4, a fluid tube 24 b 5, and a fluid tube 24 b 3. The fluid tube 24 b 4 is connected to the second connection fluid tube 22 b, the fluid tube 24 b 5 is connected to the first discharge port 34 a and the second discharge port 34 b of the first control valve 20B, and the fluid tube 24 b 3 connects the operation fluid tank 15 to the connecting portion of the fluid tube 24 b 4 and the fluid tube 24 b 5.

The internal fluid tube 81 a is a fluid tube provided on the first control valve 20B and communicated with the first connection fluid tube 22 a. In particular, when the first control valve 20B is set to the second position 20 b 2, the internal fluid tube 81 a is a fluid tube connecting the second port 36 of the first control valve 20B to the first output port 43 a of the first control valve 20B.

The external fluid tube 81 b is a fluid tube communicated with the internal fluid tube 81 a and connected to the second control valve 20C. The external fluid tube 81 b connects the first output port 43 a of the first control valve 20B to the first input port 44 a of the second control valve 20C, and connects the second output port 43 b of the first control valve 20B to the second output port 43 b of the first control valve 20B. The middle portion of the external fluid tube 81 b is connected to the central fluid tube 73 c.

In other words, the external fluid tube 81 b and the central fluid tube 73 c are connected to each other at a middle portion. In the external fluid tube 81 b, a check valve 29 b is provided between a connecting portion 93 where the external fluid tube 81 b and the central fluid tube 73 c are connected to each other and the second control valve 20C. The check valve 29 b allows the hydraulic fluid to flow from the connecting portion 93 to the second control valve 20C, and prevents the hydraulic fluid from flowing from the second control valve 20C to the connecting portion 93.

In addition, in the external fluid tube 81 b, a check valve 94 is provided between the connecting portion 93 and the first control valve 20B. The check valve 94 allows the hydraulic fluid to flow from the first control valve 20B to the connecting portion 93, and prevents the hydraulic fluid from flowing from the connecting portion 93 to the first control valve 20B.

As described above, when the first control valve 20B is set to the second position 20B2 that is the side position, the supply fluid is supplied to the second input port 42 b, and the supply fluid passes through the second connection fluid tube 22 b and then is supplied to the first hydraulic actuator 17.

On the other hand, when the first control valve 20B is set to the second position 20 b 2, the return fluid discharged from the second port 17 e of the first hydraulic actuator 17 passes through the first fluid tube 81, that is, through the first connection fluid tube 22 a, the internal fluid tube 81 a, and the external fluid tube 81 b, and flows toward the second control valve 20C.

Meanwhile, the hydraulic system of the working machine is provided with a third fluid tube 90. The third fluid tube 90 is a fluid tube configured to return the return fluid to the first control valve 20B again through the first fluid tube 81, the return fluid flowing from the first control valve 20B to the second control valve 20C.

In particular, the third fluid tube 90 is a fluid tube configured to return the return fluid to the input port of the first control valve 20B (the first input port 42 a and the second input port 42 b), the return fluid being discharged from the first output port 43 a of the first control valve 20B and flowing through the external fluid tube 81 b.

For example, when the first control valve 20B is in the second position 20 b 2, which is one of the side positions, the third fluid tube 90 is a fluid tube connecting the third output port 43 c of the first control valve 20B to the third input port 42 c of the first control valve 20B.

In other words, in the case where the first control valve 20B is in the second position 20 b 2, the third fluid tube 90 and the second fluid tube 72 are connected to each other. It is preferred that the third fluid tube 90 is provided with a throttle portion 91 configured to reduce the flow rate of the operation fluid.

As described above, when the first control valve 20B is set to the second position 20 b 2 that is the side position, the supply fluid is supplied to the second input port 42 b, and the supply fluid passes through the second connection fluid tube 22 b and is supplied to the first hydraulic actuator 17.

On the other hand, when the first control valve 20B is set to the second position 20 b 2, the return fluid discharged from the second port 17 e of the first hydraulic actuator 17 passes through the internal fluid tube 81 a and the external fluid tube 81 b, and flows toward the second control valve 20C.

Consider the following case where the return fluid passes through the first fluid tube 81, the auxiliary control valve 20C is switched to the first position 20 c 1 or to the second position 20 c 2, and thereby the hydraulic actuator 16 fails to be operated due to an external force, the hydraulic actuator 16 fails to be operated when the hydraulic actuator 16 constituted of a hydraulic cylinder reaches an end portion (an end) of the hydraulic cylinder, the supplying of the operation fluid is stopped, or the like under a condition where the hydraulic actuator 16 of the auxiliary attachment is in operation.

In other words, a case will be considered where the return fluid passes through the first fluid tube 81 and no hydraulic fluid is introduced into the first input port 44 a and the second input port 44 b of the auxiliary control valve 20C.

Under such states, since the return fluid in the first fluid tube 81 has no way to flow in the case where the third fluid tube 90 is not provided to the first control valve 20B, a pressure on the bottom side of the first hydraulic actuator 17 communicated with the first fluid tube 81 is increased. When the pressure on the bottom side of the first hydraulic actuator 17 is increased, a pressure on the rod side of the first hydraulic actuator 17 is also increased.

When the cross sectional areas on the bottom side and on the rod side are compared with each other inside the first hydraulic actuator 17, the sectional area on the bottom side is larger than the cross sectional area on the rod side. As the result, when the first hydraulic actuator 17 is stretched due to the pressure increasing on the bottom side of the first hydraulic actuator 17, the pressure increasing on the rod side will be relatively large.

For example, when the above-described situation occurs in the case where the first hydraulic actuator 17 and the third hydraulic actuator 14 are operated in combination, the operation of the first hydraulic actuator 17 may be delayed.

On the other hand, when the operation fluid is not introduced into the first input port 44 a and the second input port 44 b of the auxiliary control valve 20C in the case where the third fluid tube 90 is employed, the return fluid in the first fluid tube 81 flows to the second fluid tube 72 through the connecting portion 93. The return fluid flowing to the second fluid tube 72 returns to the input port (the first input port 42 a and the second input port 42 b) through the connecting portion 63.

In this manner, the return fluid in the first fluid tube 81 returns to the first control valve 20B again through the second fluid tube 72 and the third fluid tube 90, and thus the first hydraulic actuator 17 can be operated smoothly.

That is, since the return fluid on the rod side of the first hydraulic actuator 17 can be returned to the bottom side of the first hydraulic actuator 17, a speed of the stretching of the first hydraulic actuator 17 can be improved.

In particular, in a case where the first hydraulic actuator (the bucket cylinder) 17 and the third hydraulic actuator (the boom cylinder) 14 are operated in combination, for example, in a case where the boom cylinder 17 is stretched and the bucket cylinder 14 is stretched (in the case where the bucket cylinder 14 is operated in the dumping manner with moving the boom 14 upward), the dumping of the bucket 11 can be performed quickly.

As shown in FIG. 5, the hydraulic system of the working machine may be provided with a discharge fluid tube 70 branched off from the internal fluid tube 61 c. The internal fluid tube 61 c is a fluid tube configured to connect the first port 31 to the second output port 41 b when the third control valve 20A is in the first position 20 a 1. The discharge fluid tube 70 is a fluid tube configured to be communicated with the first discharge port 33 a in the case where the first control valve 20A is in the first position 20 a 1.

The discharge fluid tube 70 is provided with a throttle portion 71 configured to reduce the flow rate of the operation fluid. The throttle portion 71 is constituted, for example, by making a part of the discharge fluid tube 70 narrower than the other portions of the discharge fluid tube 70. In other words, the throttle portion 71 constituted by making the cross-sectional area of a portion through which the operation fluid flows smaller than the other portions in the discharge fluid tube 70.

Thus, since a part of the return fluid is discharged by the discharge fluid tube 70, the third hydraulic actuator 14 can be smoothly operated. Meanwhile, the configuration of the throttle portion 71 is not limited to the example described above.

In the above description, the embodiment of the present invention has been explained. However, all the features of the embodiments disclosed in this application should be considered just as examples, and the embodiments do not restrict the present invention accordingly. A scope of the present invention is shown not in the above-described embodiments but in claims, and is intended to include all modifications within and equivalent to a scope of the claims.

In the embodiment described above, the operation fluid is discharged to the operation fluid tank, but the operation fluid may be discharged to other components. That is, the fluid tube configured to discharge the hydraulic fluid may be connected to a portion other than the operation fluid tank, for example, the fluid tube may be connected to a suction portion of the hydraulic pump (a portion configured to suck the operation fluid), and the fluid tube may be connected to other portions.

In the embodiment described above, the control valve is a three-position switch valve. However, the number of switching positions is not limited, and the control valve may be constituted of a two-position switch valve, a four-position switch valve, or other switch valves. In the embodiment described above, the hydraulic pump is constituted of a constant-displacement pump. However, the hydraulic pump may be constituted of a variable displacement pump configured to move a swash plate to change a discharge amount, or may be constituted of another hydraulic pump, for example.

In addition, the first hydraulic actuator, the second hydraulic actuator, the third hydraulic actuator, the first control valve, the second control valve, and the third control valve are not limited to the examples of the embodiments described above, and it is only required to be provided in the working machine 1. 

What is claimed is:
 1. A hydraulic system of a working machine comprising: a hydraulic pump to output an operation fluid; a first hydraulic device; a second hydraulic device; a first control valve to control the first hydraulic device, the first control valve comprising a first input port, a second input port, a third input port, an output port, a first communication port, a second communication port, a first bypass port, a second bypass port, a first discharge port, a second discharge port, an internal central fluid tube connecting between the third input port and the output port, a first connection fluid tube connecting between the first communication port and the first bypass port, a second connection fluid tube connecting between the second communication port and the second bypass port, a first branched fluid tube connecting between the first connection fluid tube and the first discharge port, and a second branched fluid tube connecting between the second connection fluid tube and the second discharge port; a second control valve to control the second hydraulic device; a first communication tube connecting between the first communication port and the first hydraulic device; a second communication tube connecting between the second communication port and the first hydraulic device; an external central fluid tube connecting between the output port and the second control valve; a bypass fluid tube connecting between the first and second bypass ports and the second control valve; a discharge fluid tube connected to the first and second discharge ports; and a setting portion disposed in the discharge fluid tube, wherein the setting portion includes one selected from a group consisting of a cooler, a check valve, a throttle, and a relief valve; and wherein the setting portion is directly connected to the first and second discharge ports, and being configured to increase a pressure of the operation fluid at the first and second discharge ports, wherein the first control valve is configured, at a first position switched from a neutral position, to flow the operation fluid from the hydraulic pump into the first hydraulic device through the first input port, the first communication port and the first communication tube, to flow the operation fluid from the first hydraulic device into the second control valve through the second communication tube, the second communication port, the second connection fluid tube, the second bypass port and the bypass fluid tube, and to flow the operation fluid having the increased pressure in the discharge fluid tube into the second control valve through the second discharge port, the second branched fluid tube, the second connection fluid tube, the second bypass port and the bypass fluid tube.
 2. The hydraulic system according to claim 1, wherein the first control valve is configured, at a second position switched from the neutral position, to flow the operation fluid from the hydraulic pump into the first hydraulic device through the second input port, a second communication port and the second communication tube, to flow the operation fluid from the first hydraulic device into the second control valve through the first communication tube, the first communication port, the first connection fluid tube, the first bypass port and the bypass fluid tube, and to flow the operation fluid having the increased pressure in the discharge fluid tube into the second control valve through the first discharge port, the first branched fluid tube, the first connection fluid tube, the first bypass port and the bypass fluid tube.
 3. The hydraulic system according to claim 2, wherein the first hydraulic device is a hydraulic cylinder configured to be stretched and shortened, and the first control valve is switched from the neutral position to the first position to stretch the hydraulic cylinder, and switched from the neutral position to the second position to shorten the hydraulic cylinder.
 4. The hydraulic system according to claim 1, wherein the first control valve is configured, at the neutral position, to flow the operation fluid from the hydraulic pump into the second control valve through the third input port, the internal central fluid tube, the output port and the external central fluid.
 5. The hydraulic system according to claim 1, wherein the first control valve further comprises a first throttle disposed in the first branched fluid tube, and a second throttle disposed in the second branched fluid tube. 